Last Stand Cannot be chained to negate a effect.
Bug reproduction steps
Normal Summon Magical Musketeer Kidbrave (Or Any Magical Musketeer Monster) Opponent activates a Effect, try to negate with Last Stand from your hand.
Screenshot OR error code
Last Stand should’ve been activated from the hand, and negated the Opponent’s Card Effect
From the Screenshot it appears as though a monster effect was activated.
If this is the case, this working properly.
Last Stand Negates a spell or trap that was activated. Monster effects are not an option to negate with Last Stand. The reason why desperado is able to be activated in hand is because it can be activated at anytime as long as your opponent controls a face up card.